The present invention relates to a failure-protection optical path switching device for switching between optical paths employed in the field of optical communication, such as an optical communication network or an optic LAN.
In an optical communication network, when a failure occurs in a working line that is transmitting optical communication signals, the line is switched to a backup line, thereby preventing a communication failure.
FIGS. 1A and 1B are views for explaining a 1+1 failure recovery system adopted in a point-to-point optical communication network. FIG. 1A is a view for explaining a case where no failure has occurred, and FIG. 1B is a view for explaining a case where a failure has occurred.
The 1+1 failure recovery system employs an optical transmitter 1, an optical receiver 2, an optical fiber coupler 3, a working line 4 constituted of an optical fiber, a backup line 5 constituted of an optical fiber, a failure-protection optical path switching device 6, and a receiving-side line 9. An optical communication signal 7 output from the optical transmitter 1 is branched into an optical communication signal 7-1 for the working line 4 and an optical communication signal 7-2 for the backup line 5. The failure-protection optical path switching device 6 is configured such that, during a normal time when no failure has occurred, the optical communication signal 7-1 from the working line 4 is transmitted to the optical receiver 2 as a received optical communication signal 8 by way of the receiving-side line 9. Meanwhile, when a failure 9 has occurred, the optical communication signal 7-2 from the backup line 5 is transmitted to the optical receiver 2 as a received optical communication signal 8 by way of the receiving-side line 9.
FIG. 2 is a block diagram of the failure-protection optical path switching device 6, which comprises the working line 4, the backup line 5, the receiving-side line 9, optical tap circuits 11-1, 11-2, photodiodes 12-1, 12-2, an optical switch 13 having two input ports and one output port, electrical lines 14-1, 14-2, electronics 15, and electrical line 16.
During a normal time, the optical communication signal 7-1 is transmitted to the receiving-side line 9 by way of the optical switch 13. At this time, a portion of the optical communication signal (generally, 5% or less of optical communication signal power) of the working line 4 is extracted in the optical tap circuit 11-1, converted into an electric signal in the photodiode 12-1, and transmitted to the electronics 15 by way of the electrical line 14-1. The electronics 15 continuously monitor electric signals from the photodiode 12-1, thereby monitoring the transmission condition of the optical communication signal 7-1 in the working line 4. If the electronics 15 fail to receive the electric signal, the electronics 15 determine that a failure has occurred in the working line 4, and transmit to the optical switch 13 an electric signal for switching the optical switch, by way of the electrical line 16. As a result, an optical path in the optical switch 13 is switched, whereby the optical communication signal 7-2 from the backup line 5 is transmitted to the receiving-side line 9 by way of the optical switch 13.
After the failure in the working line 4 is eliminated, electric signals are transmitted from the photodiode 12-1 again. Accordingly, the electronics 15 transmit to the optical switch 13 an electric signal for switching the optical switch, thereby returning the condition so that the optical communication signal 7-1 from the working line 4 is transmitted to the receiving-side line 9. Thus, the failure in the optical communication network is recovered.
Meanwhile, similar to the case of the working line 4, the electronics 15 continuously monitor electric signals input to the backup line 5, by way of the optical tap circuit 11-2 and the photodiode 12-2, thereby monitoring a transmission condition of the optical communication signal 7-2 in the backup line 5.
FIG. 3 is a view for explaining a conventional example device into which the block diagram of a failure-protection optical path switching device shown in FIG. 2 is embodied. The conventional failure-protection optical path switching device comprises optical fiber couplers 21-1 and 21-2 serving as optical tap circuits, photodiodes 22-1 and 22-2, an optical switch 23, electrical lines 24-1 and 24-2, electronics 25, and electrical line 26. These components are mounted onto a printed board 28. The optical fiber couplers 21-1 and 21-2, the photodiodes 22-1 and 22-2, and the optical switch 23, respectively, are components having fiber pigtails. Therefore, as illustrated, the components are connected in optical fiber connecting sections 27-11, 27-12, 27-21, and 27-22 by means of fusion or adhesion.
The photodiodes 22-1, 22-2, and the electronics 25 are connected by way of the electrical lines 24-1, 24-2. The electronics 25 and the optical switch 23 are connected by way of the electrical line 26. Fiber pigtails of the optical fiber couplers 21-1, 21-2, and those the optical switch 23 are connected with optical connectors 29-1, 29-2, and 29-3 as shown in the drawing. The conventional failure-protection optical path switching device configured as above has a function of switching to the backup line 5 in the event of a failure in the working line 4, thereby transmitting an optical communication signal to the receiving-side line 9 without interruption.
Reduction in footprint has recently become an important requirement for optical communication equipment. According to a general rule, the smaller the volume of optical communication equipment, the lower the cost and the less work required for installation. Accordingly, miniaturization of a failure-protection optical path switch device which is to be incorporated in the optical communication equipment is also required.
However, a conventional failure-protection optical path switch device has a disadvantage of being of large size and expensive.
The optical fiber couplers, the photodiodes, and the optical switch respectively assume the form of independent components; and each of the components requires packaging for ensuring reliability. Accordingly, the respective components are increased in size, and require materials and man-hours for packaging, thereby becoming expensive.
In addition, each of the components includes a fiber pigtail. Accordingly, the components must be connected by means of fusion or adhesion between the fibers; however, since at least about 3 cm of work space is required to connect the fibers, the components cannot be disposed close to each other, whereby the device becomes large. Furthermore, since connection of optical fibers within a small space requires a high level of skill, such work is expensive.
Meanwhile, in FIG. 3, for the sake of simplicity, storage of slack optical fiber is not illustrated. However, since the optical fiber cannot be bent at sharp angles, storage of slack fiber for allowing the optical fiber a margin is required. Accordingly, the failure-protection optical path switching device is further increased in size.
For the above reasons, the conventional failure-protection optical path switch device is of large size and expensive.